Add caching of pi-gen artifacts

[usimd]

Adds a new feature to allow caching of pi-gen build container. If a cache hit is found the container is loaded back into the Docker daemon and pi-gen is instructed to continue from the existing container.

[codecov]

Codecov Report

Attention: Patch coverage is 22.93578% with 84 lines in your changes missing coverage. Please review.

Project coverage is 84.82%. Comparing base (b771736) to head (fb235af).

Files with missing lines	Patch %	Lines
src/cache.ts	15.00%	51 Missing ⚠️
src/actions.ts	37.03%	17 Missing ⚠️
src/cache-key.ts	33.33%	12 Missing ⚠️
src/main.ts	0.00%	2 Missing ⚠️
src/post.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #106       +/-   ##
===========================================
- Coverage   98.42%   84.82%   -13.61%     
===========================================
  Files          13       16        +3     
  Lines         509      593       +84     
  Branches      120      125        +5     
===========================================
+ Hits          501      503        +2     
- Misses          8       90       +82     

Flag	Coverage Δ
unittests	84.82% <22.93%> (-13.61%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.